Can you please give us more information on what exactly you are looking for? How would you define a "low key wedding"? What sort/quality of food do you want to serve your guests, what facilities are you looking for (music, dance floor, outdoor terrace, you name it), can you give us an idea of what budget you're working with? Can you compromise on the location or does it absolutely have to be in (the center of?) Amsterdam?
Speaking from my own experience (we organized our wedding a couple of years ago in our hometown, not far from Amsterdam), it makes a lot of difference what expectations you have, so do ask for all the options once you've decided on a venue - we managed to bring down the actual expenses by 30% from the first quotes only by shopping around a bit and having a critical look at what we wanted and - more importantly, since those venue owners will happily convince you that you need to order more, more, more to make your wedding the greatest day of your life - what not.